Friday, July 28, 2017

A pair of Pacific tropical are participating in a bizarre, circular
dance known as the Fujiwhara effect, generating high surf along the
Southern California coast just days after a similar interaction
involving separate tropical cyclones in the western Pacific Ocean.
(MORE: Hurricane Central)
Tropical Storm Hilary and Tropical Storm Irwin, are, fortunately, no threat to Mexico's Pacific coast.

Current Infrared Satellite Image

Their centers are now sufficiently close - less than 510 miles apart
- that a phenomenon meteorologists call the Fujiwhara effect kicks in.Named after a Japanese researcher who
discovered this in experiments with water in the early 1920s, the
Fujiwhara effect details how two tropical cyclones less than 900 miles
apart rotate counter-clockwise about one another.
Think of the teacup ride at Disney or
the Tilt-a-Whirl at your local county fair, but with tropical systems
instead. In the teacup ride, adjacent teacups can not only spin, but
revolve about each other.
In this case, Irwin, the southern storm of the pair, has temporarily
stalled, but will soon get pulled north and will revolve
counterclockwise around the circulation of Hilary this weekend,
according to the latest forecast guidance.
(FORECAST PATHS: Hilary | Irwin)

ECMWF
(European) model forecast from July 27, 2017, of the expected Fujiwhara
effect of tropical cyclones Irwin and Hilary. Lower pressure is denoted
by the deeper orange and red contours. Higher pressure is shown by the
brighter teal, aqua colors.

Separate West Pacific Dance

More than 5,000 miles away, Typhoon Noru, the first typhoon of 2017,
teamed up with another tropical cyclone named Kulap in a separate
Fujiwhara effect.
While Kulap had degenerated to a remnant, one could still pick out
its leftover circulation in Himawari-8 visible satellite imagery on July
27, south-southwest of Noru.

The
remnant of former Tropical Storm Kulap and Typhoon Noru are shown in
this visible satellite image from the Himawari-8 satellite on July 27,
2017.(JMA)

Tuesday, thanks, in part, to the Fujiwhara interaction, Noru crossed
its previous path from last week completing an oval-shaped loop, and
will now migrate westward.
Thanks to weak steering winds over the northwest Pacific, Noru may
loaf and lollygag near Iwo To (previously known as Iwo Jima) well into
next week.

Noru Path History and Forecast Path

We still can't rule out an eventual land impact in Japan or
southeastern Russia, but that may not come until late next week or the
following weekend. In the meantime, Noru may intensify, and is likely to
at least generate large swells that will reach the Japanese Pacific
coast and persist into next week.
Satellite loops of these dual Fujiwhara events should be compelling to meteorologists and weather enthusiasts alike.To see this happen once a season isn't unusual,
according to a 2014 study in the western Pacific Ocean, but for this to
happen in two separate areas within days is very unusual.Jonathan Erdman is a senior meteorologist at weather.com
and has been an incurable weather geek since a tornado narrowly missed
his childhood home in Wisconsin at age 7. Follow him on Facebook and Twitter.MORE: Atlantic Basin Retired Hurricanes and Tropical Storm Names

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